1. Field of the Invention
The present invention relates to a fuel injection pump plunger, and in particular to a fuel injection pump plunger wherein the structure has been improved by eliminating the furrow on the inclined lead.
2. Description of the Related Art
In fuel injection pumps fitted to diesel engines, and particularly in on-line fuel injection pumps, it has hitherto been normal practice to control the amount of fuel injected by creating on the outer periphery of the plunger an inclined lead formed from a spiral groove, and to create a spill port on a timing sleeve in a position which coincides with the position of this inclined lead.
Instances are provided by Japanese Patents S631988!-503076 and H51993!-87011, and by Japanese Utility Model H41992!-100063.
There follows an explanation with reference to FIGS. 5 and 6, in which the abovementioned Japanese Utility Model H41992!-100063 is taken as an example. FIG. 5 is a cross-sectional view of the principal part of a conventional fuel injection pump 1 at commencement of fuel injection, while FIG. 6 is a cross-sectional view of the principal part at conclusion of fuel injection. The fuel injection pump 1 has a delivery valve housing or pump housing 2 and a plunger barrel 3 located within this pump 2 housing. Inside is formed a fuel reservoir chamber 4.
Between this pump housing 2 and plunger barrel 3 is located a plunger 5 in such a manner that it is capable of rotation and reciprocating motion. Above the plunger 5 is formed a high-pressure fuel pressure chamber or plunger chamber 6, which connects with a delivery valve (not shown in the drawing).
The plunger 5 has a fuel suction and exhaust port 7, a central fuel passage 8 which connects with the fuel suction and exhaust port 7 and runs to the plunger chamber 6, a peripheral furrow 9 which connects with the fuel suction and exhaust port 7, and a peripheral inclined lead 10 which connects with this furrow 9.
A timing sleeve 11 (control sleeve) is fitted externally to the plunger 5. This timing sleeve 11 allows the pre-stroke (the stroke from the bottom dead point of the plunger 5 to commencement of injection) to be modified by permitting vertical motion with the aid of a control rod (not shown in the drawing) so as to alter the position relative to the plunger 5.
A spill port 12 is formed in the timing sleeve 11 in the direction of its radius. This spill port 12 is formed in a position which coincides with that of the inclined lead 10 in the direction of the axis of the plunger 5.
A control rack 13 is provided to allow the plunger 5 to rotate around its axis in relation to the timing sleeve 11, and it is possible for the spill port 12 and the inclined lead 10 to coincide in the direction of the axis of the plunger 5 even if the plunger 5 rotates as a result of the operation of the control rack 13.
In a fuel injection pump 1 of this structure, the lowering of the plunger 5 causes the fuel within the fuel reservoir chamber 4 to be admitted through the fuel suction and exhaust port 7, while its raising causes the fuel suction and exhaust port 7 to close by the action of the lower edge 11A of the timing sleeve 11, thus commencing compression of the fuel (FIG. 5).
When the plunger 5 rises further until the inclined lead 10 coincides with the spill port 12, the plunger chamber 6 and the fuel reservoir chamber 4 connect via the central fuel passage 8, fuel suction and exhaust port 7, furrow 9 and inclined lead 10, with the result that a prescribed amount of fuel spills from the spill port 12 into the fuel reservoir chamber 4, thus concluding fuel injection (FIG. 6). The plunger 5 continues to rise, the furrow 9 protrudes beyond the upper edge 11B of the timing sleeve 11, and as a result fuel spills from this furrow 9 also.
Control of the amount of fuel injected is achieved by operating the control rack 13 to allow the plunger 5 to rotate about its axis and alter the position at which the inclined lead 10 and spill port 12 engage, thus adjusting the effective stroke S of the fuel delivery (FIG. 5).
It is also possible to advance or retard the timing of the fuel injection by operating the timing sleeve 11 up and down in order to adjust the pre-stroke.
FIG. 7 is a side elevation of the principal part showing the relationship between the furrow 9 of the plunger 5 and the spill port 12 of the timing sleeve 11. The purpose of the furrow 9 is to ensure this no-injection state.
In other words, when the plunger 5 is rotated in relation to the timing sleeve 11 and positioned so that the spill port 12 can coincide with the furrow 9, if the plunger 5 is above a prescribed position, the plunger chamber 6 and the fuel reservoir chamber 4 are connected with each other via the central fuel passage 8, fuel suction and exhaust port 7, furrow 9 and spill port 12, and the plunger 5 is unable to implement the action of compressing the fuel. Thus a state of no-injection is achieved, wherein it is possible to halt the fuel delivery function of the fuel injection pump 1 in emergencies and as desired at other times when this is necessary.
Moreover, inasmuch as the area of the passage is greater than the prescribed value, the furrow 9 also has the function of avoiding secondary injection by ensuring that it does not act as a throttle to fuel passing through when fuel spills from the spill port 12.
However, there is a problem in that the timing sleeve 11 becomes deformed as a result of the fact that in order for it to achieve this function the groove 9 occupies a relatively large proportion of the outer periphery of the plunger 5.
In other words, FIG. 8 is an end cross-section of the plunger 5 and the timing sleeve 11. As the drawing shows, the timing sleeve 11 becomes deformed and assumes an elliptical shape (the imaginary line in the drawing) as a result of the pressure of the fuel acting from the central fuel passage 8 of the plunger 5 on the inclined lead 10 and especially on the furrow 9. This tendency is aggravated as the pressure of the fuel injection pump increases, leading to problems of locking between the plunger 5 and the timing sleeve 11, or causing damage to the timing sleeve 11.
With the foregoing in view, it is an object of the present invention to provide a fuel injection pump plunger wherein it is possible to prevent deformation of the timing sleeve in the face of high fuel pressure.
It is a further object of the present invention to provide a fuel injection pump plunger wherein it is possible to ensure no-injection state even with elimination of the furrow which is the chief cause of deformation of the timing sleeve.
It is yet a further object of the present invention to provide a fuel injection pump plunger wherein it is possible to ensure no-injection state by ensuring the area of the aperture of the spill port in no-injection state, and to avoid secondary injection.